1. Field
Disclosed is a metal nanoparticle that may be used for photothermal therapy, and a method for producing the same.
2. Description of the Related Art
Numerous free electrons exist inside metal conductors. Since such free electrons are not bound to metal atoms, and thus they may easily respond to a specific stimulus from an external environment. In particular, in the case of nano-sized metals, surface plasmon resonance characteristics appear as a result of the behavior of free electrons, giving unique optical characteristics to metal nanoparticles. Surface plasmon is a phenomenon in which electrons in a metal oscillate as a group when light is incident between the surfaces of conducive metal nanoparticles and dielectric materials, such as air or water, and the oscillation frequency of the electrons vibrating with respect to the nucleus resonate with a certain specific frequency of incident light. The interaction between light and metal nanoparticles is very strong and metal nanoparticles have a much higher absorption coefficient than regular organic dyes at a resonance frequency. Since the resonance frequency varies based on the size, form, or surface characteristics of particles and dispersed solvents, efforts to make metal nanoparticles having various sizes, forms, and surface characteristics are in progress in order to apply such metal nanoparticles to, for example, optical sensors or light condensers.
Recently, photothermal therapy utilizing the light condensing effect of gold nanoparticles has arisen as a potential biotechnical application. Photothermal therapy is a therapeutic method in which light energy is converted into heat energy that attacks the cells that are to be treated. The light condensed on the surface of gold nanoparticles may be emitted via various routes, including the heat-accompanied processes of electron-lattice vibration and electron-electron scattering. Then, the heat energy that is locally emitted from the gold nanoparticles may be sufficient to kill target cells because of the excellent light condensing effect and the large surface area to volume ratio of gold nanoparticles. In addition, when the local heat emission is controlled by selectively limiting or increasing the amount of light that is condensed on the gold nanoparticles, this permits for the selective treatment or killing of cancer cells or cells of inflammatory sites while leaving normal cells undamaged.
A nano structure useful in cancer selective photothermal therapy, using a pH or temperature sensitive surface ligand to alter the surface structure or surface electron charge of gold nanoparticles, is also being developed. However, there remain problems to be solved, such as the toxicity that results from surface ligands that are not naturally present in the circulatory system.